Some ideas off top of my head:
1. Use an OD set-up off an old Borg Warner 3-speed. Such as used on old Fords and other makes in the 50's.
2. Use a OD set-up that they adapt for old Model As, I think it may be Volvo parts inside?
3. Use an automatic trans planetary gear set and make a custom housing.
4. Custom gears for your Honda trans? reversing the position of the 4th or 5th gear (or whatever the next to highest gear you have that is not straight through 1:1), but reversed so it is overdriving rather than underdriving. Does that makes sense in my description? Does your trans have a factory OD top gear, if so just try to make it taller.
You certainly do not need a big Gear Vendors type unit.
I guess your problem is can not get a tall enough rearend gear ratio?
